Block copolymers are used, or are considered to be applied as molded resin, binding agent/adhesive agent, support of adhesive tape, resin with improved shock-resistance, tackifier, dispersant, surface modifier, compatibilizer, separation membrane, elastic fiber, high molecular surfactant, pharmaceutical preparation, medical material, antifouling paint, superhydrophobic membrane, etc. Further, applications in the field of electric and electronic, including photoelectric conversion element, light emitting element, display, light modulation element, organic FET element, capacitor, liquid-crystal oriented film, reversible thermosensitive recording medium, hologram optical element, optical recording medium, film for smart windows, and anisotropic conductive material, are considered recently.
Among these, it is considered to use the microphase separation structure of a block copolymer as a mask, to transcript its pattern, processing at a nanoscale base, and to apply for producing recording devices such as flash memory, optical recording disk, and hard disk, or light emitting elements (for example, see Patent Document 1). In this case, as the microphase separation structure is used as a mask, it is desirable that the size of the domain of the phase separation structure can be controlled arbitrarily.
Generally, a microphase separation structure is a phenomenon observed in a polymer which molecular weight is several tens of thousands or more, and has a narrow molecular weight distribution, wherein polymers with different polarity or being incompatible with each other are bound as a block. For example, sea-island structure, columnar structure, and lamellar structure are known, and the domain size is about 10 to 100 nm. The microphase separation structure are not expressed when the polarity difference between polymers having different polarity is too small. On the contrary, when the difference is too large, not a microphase separation structure, but a macrophase separation structure is expressed. Therefore, an appropriate polarity difference is required. Normally, the domain structure in the microphase separation structure is determined by the composition ratio of a block copolymer, and the domain size is determined by the molecular weight of the block copolymer.
Further, it is known that an intermediate layer called the interface layer exists in the periphery of the domain of the microphase separation structure. The interface layer tends to be larger when the polarity difference among polymers having different polarity is smaller.
The most commonly known block copolymer expressing a microphase separation structure can be exemplified by a styrene/methyl methacrylate block copolymer. The interface layer of this styrene/methyl methacrylate block copolymer is relatively large. Further, for example, when trying to make the domain size of the sea-island structure expressed by this block copolymer expresses to be about 20 nm or less, it is necessary to reduce the molecular weight to several ten thousands or less. However, in this case, there is a problem that almost no microphase separation structure is observed.
Recently, materials for use in the electric and electronic field have a high-density, as represented by recording devices, and when applying the microphase separation of a block copolymer for manufacturing such devices, it is necessary to make the domain size or interface layer as small as possible. Thus, such block copolymers were awaited.
Block copolymers forming microphase separation structure are exemplified in the following.
Patent Document 2 describes a method to form a microphase separation structure by using a diblock copolymer wherein polystyrene chain and poly(methyl methacrylate) chain are linked. The diblock copolymer herein used has an average molecular weight of 65,000 (it is unclear whether it is a mass average molecular weight or number average molecular weight), and the ratio of poly(methylmethacrylate) chain in the copolymer is 20 wt % or 80 wt %. After forming a film of the block copolymer on a basal plate, heating at 210° C. for 4 hours, and further at 135° C. for 40 hours, a microphase separation structure is expressed. The size of the dotted parts of the microphase separation structure (domain size) is 30 nm at minimum.
Patent Document 3 describes a method to form a microphase separation structure by using a diblock copolymer consisting of polystylene and polyisoprene. The diblock copolymer has a mass average molecular weight (Mw) of 290,000, Mw/Mn=1.12, and volume ratio of polyisoprene is 29.7%. By making a film of the diblock copolymer on a basal plate, and heating at 170° C. for hours, a microphase separation structure having a cylinder structure is expressed. The size of the cylinder consisted of polyisoprene is 20 nm.
Nonpatent Documents 1 and 2 describe methods to form a microphase separation structure by using a triblock copolymer consisting of polystyrene (S), poly(2-hydroxyethyl methacrylate)(H) and poly(methyl methacrylate) (M). The documents describe those with a number average molecular weight (Mn) of 82,000 to 134,000, Mw/Mn=1.02 to 1.04. Among these, by forming a film of those with a number average molecular weight (Mn) of 134,000 on a basal plate, and heating at 190° C. for 5 days, a microphase separation structure is expressed. The size of dots is about 20 nm.
However, as it is seen from these documents, so far, there was no example of a block copolymer with a mass average molecular weight or number average molecular weight of 50,000 or less, and which forms a clear microphase separation structure.    [Patent Document 1] Japanese Laid-Open Patent Application No. 2003-258296    [Patent Document 2] Japanese Laid-Open Patent Application No. 2005-118936    [Patent Document 3] Japanese Laid-Open Patent Application No. 2006-327853    [Non Patent Document 1] Macromolecules 2001, 34,7477-7488    [Non Patent Document 2] Macromolecules 2002, 35,1319-1325